Swindle involving one currency item (4)
I believe the answer is:
coin
'currency item' is the definition.
(coins are used as currency)
'swindle involving one' is the wordplay.
'swindle' becomes 'con' (synonyms).
'involving' means one lot of letters goes inside another.
'one' becomes 'i' (Roman numeral).
'con' going around 'i' is 'COIN'.
(Other definitions for coin that I've seen before include "Make up" , "Invent (a new phrase)" , "Penny, say?" , "Create (phrase); metal token" , "Metal piece of money" .)